1. Field of the Invention
The present invention relates to a liquid ejector and, more particularly, to a head for use in an ink jet printer.
2. Description of the Background Art
Historically, an ink jet printer head has employed a process for introducing acoustic waves generated from a piezoelectric transducer into ink to eject droplets of ink or sprays of ink using the acoustic energy of the acoustic waves. A head for increasing the density of the acoustic energy by focusing acoustic waves to enhance the efficiency of ink ejection has been considered.
FIG. 19 is a cutaway view in perspective of a conventional ink jet printer head. FIG. 20 is a cross-sectional view taken along the xz plane of FIG. 19.
An ink tank 110 has a recess for storing ink 130 and having a bottom surface serving as a reflecting surface 111. The reflecting surface 111 defines a parabola in cross section taken along the xz plane. A plurality of piezoelectric transducers 120 arranged in two rows, with the piezoelectric transducers 120 in each row arranged in the y direction, are disposed over (in the positive x direction of) the recess of the ink tank 110. A gap between the two rows defines an ejection opening 119. Each of the piezoelectric transducers 120 comprises an upper electrode 121 and a lower electrode 122 which are connected to an alternating-current power supply 125 through interconnect lines 123 and 124, respectively. For purposes of illustration, the interconnect lines 124 and the alternating-current power supply 125 are not shown in FIG. 19.
The piezoelectric transducers 120 introduce acoustic waves 126 that vibrate in a thickness-longitudinal direction into the ink 130. The acoustic waves 126 travel in the recess in the negative x direction, and then are reflected from the reflecting surface 111. If the ejection opening 119 is provided adjacent the focal point 112 of the parabola defined by the reflecting surface 111, the acoustic waves 126 are focused on the focal point 112 in an in-phase condition to increase the density of the acoustic energy of the acoustic waves 126 at the ejection opening 119, achieving efficient ejection of an ink droplet 131 from the ejection opening 119.
The piezoelectric transducers 120 adjacent to each other are independently driven to eject the ink droplet 131 at a desired position on the y-axis in the ejection opening 119.
The conventional head having the above described structure presents following drawbacks:
(1) The size of the ejection opening 119 which is defined as a gap between the two rows of piezoelectric transducers 120 is difficult to control with high accuracy. PA1 (2) Since the piezoelectric transducers 120 are provided adjacent the ejection opening 119, the acoustic waves 126 focused in the ejection opening 119 and the vibration of the piezoelectric transducers 120 are not always in phase and are liable to attenuate each other. PA1 (3) The interconnect lines 124 required for the lower electrodes 122 are difficult to install. PA1 (4) An intake passage for supplying the ink 130, which is generally provided in the bottom of the recess for storing the ink 130, must be formed in a position so as not to impair the configuration of the reflecting surface 111. The intake passage is easy to form so as to extend in the y direction, but impairs the reflecting surface 111 if formed so as to extend in the z direction. PA1 (5) The acoustic waves 126 travel once in the negative x direction. Then, the paths of the acoustic waves 126 with components oriented in the positive x direction are reflected at acute angles from the reflecting surface 111. Thus, a large amount of acoustic energy transmitted through the reflecting surface 111 is lost.